There are many occasions when large structures have to be inspected, cleaned or repaired This can be a dangerous and time consuming activity involving suspended work platforms or the erection of scaffolding. An alternative approach is to use a robot which can climb the structure carrying with it the tools and equipment to perform the required task. Such a robot must be light so that its weight does not strain the structure, yet rugged enough to work in an exterior environment and powerful enough to carry the necessary payload. A suitable robot has the potential for achieving considerable cost benefits compared with traditional methods.